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Free CMD Practice Questions

10 free, exam-style Certified Medical Dosimetrist (CMD) practice questions with answers and explanations. No signup required. Work through them below, then take the full free CMD practice test to study every exam domain.

Question 1

A tumor is prescribed 60 Gy in 30 fractions. Using an alpha/beta ratio of 10 Gy, what is the biologically effective dose (BED) for this regimen?

  1. 66 Gy
  2. 72 Gy
  3. 100 Gy
  4. 120 Gy
Show answer & explanation

Correct answer: B - 72 Gy

Question 2

During contouring, the physician outlines the volume that contains the GTV plus regions of suspected subclinical microscopic disease, before any margin for organ motion or setup error is added. Which volume has been defined?

  1. Clinical target volume (CTV)
  2. Internal target volume (ITV)
  3. Planning target volume (PTV)
  4. Treated volume
Show answer & explanation

Correct answer: A - Clinical target volume (CTV)

Question 3

Two competing IMRT prostate plans cover the target equally. Plan A has a conformity index of 1.05; Plan B has a conformity index of 1.80. Considering conformity alone, what does Plan B's value indicate relative to Plan A?

  1. The dose distribution is more homogeneous within the target
  2. The prescription isodose conforms more tightly to the target
  3. More normal tissue is receiving the prescription dose
  4. The target periphery is being systematically underdosed
Show answer & explanation

Correct answer: C - More normal tissue is receiving the prescription dose

Question 4

For a 6 MV photon beam in soft tissue, which interaction between radiation and matter is responsible for the majority of energy deposition?

  1. Photoelectric effect
  2. Pair production
  3. Compton scattering
  4. Coherent (Rayleigh) scattering
Show answer & explanation

Correct answer: C - Compton scattering

Question 5

An Ir-192 source (half-life 73.8 days) is calibrated for an HDR unit. Approximately 148 days later, what percentage of the original activity remains?

  1. 50%
  2. 12.5%
  3. 75%
  4. 25%
Show answer & explanation

Correct answer: D - 25%

Question 6

A rectangular photon field measures 6 cm x 18 cm. Using the 4 x Area / Perimeter approximation, what is its equivalent square field size?

  1. 12 cm
  2. 9 cm
  3. 6 cm
  4. 18 cm
Show answer & explanation

Correct answer: B - 9 cm

Question 7

A lung tumor plan is being calculated near a large air-filled cavity. Which dose calculation algorithm is expected to be the LEAST accurate in this low-density region?

  1. Pencil beam
  2. Acuros XB (grid-based Boltzmann)
  3. Collapsed-cone convolution/superposition
  4. Monte Carlo
Show answer & explanation

Correct answer: A - Pencil beam

Question 8

In the Manchester system for intracavitary treatment of cervical cancer, where is the reference dose point known as Point A located?

  1. 2 cm superior to the external cervical os and 2 cm lateral to the canal
  2. 5 cm lateral to the patient midline at the level of the cervical os, on the pelvic wall
  3. At the surface of the vaginal cylinder where the mucosa is contacted
  4. At the tip of the intrauterine tandem within the fundus of the uterus
Show answer & explanation

Correct answer: A - 2 cm superior to the external cervical os and 2 cm lateral to the canal

Question 9

A dosimetrist informs the radiation safety officer that she is pregnant and wishes to declare her pregnancy. Per U.S. NRC regulations (10 CFR Part 20), what is the dose-equivalent limit to the embryo/fetus for the entire declared pregnancy?

  1. 5 rem (50 mSv)
  2. 0.1 rem (1 mSv)
  3. 1.5 rem (15 mSv)
  4. 0.5 rem (5 mSv)
Show answer & explanation

Correct answer: D - 0.5 rem (5 mSv)

Question 10

A clinic wants to confidentially report a near-miss event to a national database so that aggregated data can improve safety across radiation oncology practices. Which system is specifically designed for this purpose?

  1. RO-ILS (Radiation Oncology Incident Learning System)
  2. The FDA MedWatch adverse-event reporting program
  3. The Joint Commission sentinel event reporting database
  4. The NRC abnormal occurrence and material event report
Show answer & explanation

Correct answer: A - RO-ILS (Radiation Oncology Incident Learning System)

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